ALBERT

Description: The poloidal mode field line resonance in the Earth's dipole magnetic field is investigated using cold plasma ideal MHD simulations in dipole geometry. In order to excite the poloidal mode resonance, we use either an initial or a continuous velocity perturbation to drive the system. The perturbation is localized at magnetic shell L = 7 with plasma flow in the radial direction (electric field component in the azimuthal direction). It is found that with the initial perturbation alone, no polodial mode resonance can be obtained and the initially localized perturbation spreads out across all magnetic L shells. With the continuous perturbation, oscillating near the poloidal resonance frequency, a global-scale poloidal cavity mode can be obtained. For the first time, a localized guided poloidal mode resonance is obtained when a radial component of electric field is added to the initial perturbation such that the curl of the electric field is everywhere perpendicular to the background dipole magnetic field. During the localized poloidal resonance, plasma vortices parallel/antiparallel to the background dipole magnetic field B(sub 0). This circular flow, elongated radially, results in twisting of magnetic field flux tubes, which, in turn, leads to the slowdown of the circular plasma flow and reversal of the plasma vortices. The energy associated with the localized poloidal resonance is conserved as it shifts back and forth between the oscillating plasma vortices and the alternately twisted magnetic flux tubes. In the simulations the eigenfunctions associated with the localized poloidal resonance are grid-scale singular functions. This result indicates that ideal MHD is inadequate to describe the underlying problem and nonideal MHD effects are needed for mode broadening.

Description: Plasma dynamics and momentum transport near an X line during time-dependent magnetic reconnection in a collisionless plasma are investigated based on two-dimensional particle simulations. We find that a weakly skewed velocity distribution is formed near the magnetic X line, leading to the presence of off-diagonal elements of the plasma pressure tensor. Let the reconnection electric field be in the y direction. The gradients of the off-diagonal elements of the pressure tensor can provide a transport of the y momentum. During the normal magnetic reconnection, the momentum transport associated with the off-diagonal terms of the pressure tensor mediates a transfer of the y momentum from the region near the X line to regions outside the X line. A period of 'reverse magnetic reconnection,' during which the plasma kinetic energy is converted into magnetic energy, is also observed in the simulation. When reverse reconnection occurs, the gradients of the off-diagonal pressure tensor elements can mediate a transfer of y momentum into the X line. It is found that the inertial term also plays a significant role in the force balance near the magnetic X line. An explanation for the origin of the off-diagonal pressure terms is also given in this paper.

Description: Particle simulations (including both ions and electrons) of the driven collisionless magnetic reconnection process at the earth's dayside magnetopause were carried out using a specially developed two-and-one-half-dimensional electromagnetic particle code with a driven inflow boundary and an open outflow boundary. The simulations were used to examine many features associated with the dayside magnetic reconnection process, including the acceleration and heating of particles and the generation of energetic particles and particle heat flux. In addition, the fluctuating electromagnetic field associated with a driven collisionless magnetic reconnection was examined and compared with the satellite observations of flux transfer events at the day-side magnetopause.

Description: The beta dependence (where beta is the ratio between plasma pressure to magnetic pressure) of the collisionless tearing instability at the dayside magnetopause current sheet was investigated analytically for several current sheet models. The results show that, when the asymmetry of the dayside magnetopause current sheet is taken into account, the beta dependence of the collisionless tearing instability at the dayside magnetopause is controlled by the magnetic field profile across the magnetopause current sheet.

Description: The driven collisionless magnetic reconnection processes at the dayside magnetopause and in the magnetotail are investigated through 2.5 D particle simulations. During reconnection, magnetic field configurations with both a single X line and multiple X lines are obtained. Magnetic reconnection enhancements, which are indicated by the peaks in the inductive electric field, are observed in the simulations. Coincident with the magnetic reconnection enhancements, bursts of energetic particles, electrons with an energy spectrum of about E exp -3.8 and ions with an energy spectrum of about E exp -4.4, are generated during the reconnection processes. Field-aligned particle heat fluxes are also generated. Intense plasma waves associated with the reconnection processes are observed. It is found that the fluctuating magnetic field has a power spectrum of about f exp -3.8 and the fluctuating electric field has a power spectrum of about f exp -1.8, respectively. A review of the simulation studies of driven collisionless magnetic reconnection and slow shocks in the magnetospheric current sheets is presented.

Description: This paper examines magnetic signatures associated with the time-dependent magnetic reconnection processes at the dayside magnetopause, using two-dimensional compressible MHD simulations. Emphasis is placed on the different flux-transfer-event (FTE) signatures generated by the bursty single X-line reconnection (BSXR) and the multiple X-line reconnection processes. It is shown that the FTE magnetic signatures are not exhibited on the magnetospheric side if the FTEs are due to the BSXR process and the ratio between the magnetic field strength in the magnetosheath to that in the magnetosphere is not less than 1.7. The simulation results are compared with satellite observations.